Assistant District Attorney Holly Broadbent, chief of Conley’s Sexual Assault Unit, recommended that Williams serve 25 to 28 years in state prison, followed by 10 years of probation upon his release. Broadbent recommended that, as conditions of his probation, he be ordered to wear a GPS monitoring device, undergo sex offender treatment and have no contact with the victim.

Judge Linda Giles imposed a term of 18 to 22 years in prison but adopted all of Broadbent’s other recommendations. Giles noted that state sentencing guidelines call for a sentence of 12 to 18 years.

“Our recommendation went well beyond the average sentencing guidelines for two reasons,” Conley said. “First, this crime was not average. It was as vicious and terrifying as can be imagined. Second, the defendant had just finished a lengthy state prison term for the same offense. He has additional convictions for crimes of violence against women. He needs to be taken off the street and away from society.

“Moreover, a review of his record suggests that he’s a candidate for civil commitment under the state’s sexually dangerous person statute, which would allow him to be held even after his release from prison.”

While the victims of any crime are asked to call 911 in an emergency.” Conley said that survivors of sexual violence in Suffolk County can also call the Boston Area Rape Crisis Center’s 24-hour hotline at 800-841-8371. The Boston Area Rape Crisis Center provides medical advocacy, legal services, counseling and other services to victims of rape and sexual assault.

Had the case proceeded to trial, Broadbent would have introduced evidence and testimony to prove that Williams followed the woman, then 28, as she approached her home in the early morning hours of Nov. 10, 2012. He followed her into her apartment building and, as she entered her apartment, forced his way inside, where he robbed her of jewelry, electronic devices and her bank card. He then sexually assaulted her at knifepoint and threatened to return and kill her if the ATM password she provided was incorrect.

The victim was able to contact a neighbor, who called 911. She was transported to an area hospital for treatment, while Boston Police sexual assault detectives undertook a search for evidence and witnesses. Among other things, they were able to retrieve footage from a bank lobby where Williams used the victim’s debit card and additional footage showing him selling her iPad and iPhone. When detectives released it to the public, they received multiple tips identifying him, leading to his arrest.

“That surveillance footage was crucial in helping us build our case,” Conley said. “Surveillance cameras can only help investigate, solve, and prosecute violent crimes, but we’re routinely delayed by hours or even days trying to get footage from private businesses. Cameras operated by city or state agencies could provide that footage on a moment’s notice without violating the privacy we enjoy as Americans.”